This invention relates to improvements in motorcycles and more particularly to a suspension and steering arrangement for the front wheel of a motorcycle.
Rear swing arm suspensions are now well known in the motorcycle industry and have become rather common in recent years. In such suspension systems, the rear wheel of the motorcycle is journaled to the end of a U-shaped fork, or swing arm. The swing am is hinged to the frame of the motorcycle and extends rearwardly. The rear swing arm and wheel undergo generally vertical swinging motion in response to road shocks and changing weight loads. The swing arm is spring loaded downwardly, typically by means of a compression spring, so that the swing arm can bear ordinary weight loads as well as road shocks. Various combinations of shock absorbers, dampers, and springs have been used to spring load and damp the swing arm. Road shocks and changing weight loads are typically transmitted via swinging motion of the swing arm to a shock absorber that incorporates a damper as well as the compression spring that provides the necessary downward force on the swing arm. There is commonly provided some mechanism for adjusting the spring force applied to the swing arm in order to adjust the ride of the motorcycle or to accommodate different riders, differing weight loads or changed road conditions.
Traditionally, front suspension systems of motorcycles have not been as well developed. Until relatively recently, motorcycles have been virtually universally equipped with a fork-type front end suspension system. The fork tubes are connected through a head assembly to a rotatable steering column which is journaled to the frame of the motorcycle. The axle of the front wheel is journaled to the lower ends of the fork tubes. Such designs have a recognized disadvantage in that all weight loads and road shocks on the front wheel are transmitted up through the front fork to the frame of the motorcycle, at a point on the frame which is well above and forward of the center of gravity of the motorcycle. This results in the front fork, the attached steering head, and the upper portions of the frame all being necessarily stronger, and thus heavier, than would be necessary to merely bear the suspension loads on the front wheel of the motorcycle. It also results in the entire front suspension system turning with the front wheel, when all that needs to be turned to effect steering is the front wheel, thus increasing the steering effort and the amount of unsprung mass of the front wheel.
In a co-pending patent application entitled, "Double Swing Arm Motorcycle Front Suspension," filed on Nov. 1, 1991 (Ser. No. 07/786,733) and naming as inventors Toyoji Tanaka, the inventor of the present invention, and additionally, Ichiro Kurawaki and Kazumasa Nakaya, and assigned to the assignee hereof, there is disclosed a motorcycle having a one-sided front swing am suspension system. The system of that application includes upper and lower control arms which are hinged to the frame of the motorcycle and which extend forwardly from the frame to a steering knuckle (also known as a kingpin). The steering knuckle extends along one side of the front wheel at a rake angle (i.e., the steering knuckle extends at an angle upwardly and rearwardly from the wheel axle to the steering column) which is similar to the rake angle of a conventional telescoping fork, and curves around the outer periphery of the wheel. A substantial rake angle is necessary and desirable to obtain satisfactory motorcycle steering response, and is also desirable because it renders the suspension most effective in absorbing road shocks.
The front wheel is journaled in a cantilevered fashion to an axle which extends transversely from the lower end of the steering knuckle. The lower control arm is arcuate and extends alongside of and around the front wheel. The lower control arm is connected to the lower end of the steering knuckle by means of a ball joint which allows the front wheel to be steered while also allowing swinging motion of the control arm. The upper control arm extends forwardly from the frame of the motorcycle and is connected to the upper end of the steering knuckle, at a location above the front wheel, also by means of a ball joint. The upper and lower control arms swing in parallel so as to absorb road shocks and weight loads on the front wheel.
A one-sided front swing arm suspension arrangement, similar in certain major respects to that just described, is also set forth in U.S. Pat. No. 4,526,249 to James G. Parker, issued on Jul. 2, 1985. Details of this suspension arrangement are disclosed in the '249 patent, which is expressly incorporated herein by reference.
It has been recognized that one primary advantage of the one-sided front swing arm suspension has been that weight and shock loads on the front wheel can be effectively borne by the motorcycle frame at a point low and close to the center of gravity of the frame, rather than at the point where the steering column is journaled to the frame.
However, as recognized in the above-identified co-pending patent application, a problem which may be encountered when employing a swing arm front wheel suspension system for a motorcycle involves the forwards and backwards lateral movement of the arrangement as the swing arms move through their respective arcs about axes defined by the points at which the swing arms connect to the motorcycle's frame. It is desirable that such forwards and backwards lateral movement be kept to a minimum.
Additionally, it has been recognized that a means for fine tuning the relative positioning between the swing arms and steering knuckle in front swing arm type suspension systems is desirable. Sometimes a rider may prefer a different camber angle of the front wheel in front swing arm arrangements. A fine tuning system could allow for the ready tuning of the suspension system until the desired camber angle of the front wheel is achieved. Of course, it is most desirable to have a fine tuning system that is easy to operate and which does not add excessive bulk or weight to a motorcycle front swing arm type suspension arrangement.
It is, therefore, an object of this invention to provide an improved suspension and steering arrangement for the front wheel of a motorcycle.
It is further an object of this invention to provide a one-sided front swing arm suspension system for a motorcycle which minimizes any forwards and backwards lateral movement of the arrangement encountered during any swinging motion of the swing arms during motorcycle operation.
It is yet another object of this invention to provide a one-sided front swing arm suspension system for a motorcycle which can be readily tuned for accurate performance.